Decay spectroscopic for nuclear astrophysics

Abstract

Abstract. In many radiative proton capture reactions important in H-burning in novae and XRBs, the resonant parts play the major role. I will show how one can use decay spectroscopy techniques to find these resonances and study their properties. I will exemplify with techniques developed at Texas A&M University to measure -and -delayed proton decay, applied to sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer. The short-lived radioactive species are produced in-flight, separated, slowed down from about 30-40 MeV/u and implanted in the middle of very thin Si detectors. This allowed us to measure protons with energies as low as 200-400 keV from nuclei with lifetimes of 100 ms or less. At the same time we measured gamma-rays up to 8 MeV with high resolution HPGe detectors. We have studied the decay of 23 Al, 27 P and 31 Cl. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and worked even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions 22 Na(p,) 23 Mg (crucial for the depletion of 22 Na in novae), 26mAl(p,) 27 Si and 30 P(p,) 31 S (bottleneck in novae and XRB burning), respectively. At the same time the decay properties were established for these 3 isotopes, which were cleanly separated here for the first time. Their lifetimes were measured; the IAS states and their decay were un-equivocally located. I will briefly show how a recent detector development allows better measurements in the critical region of proton energies 100-400 keV.